WASHINGTON – Mainstream conservatives ran the table in Senate Republican primaries as tea party upstarts lost all six challenges to GOP incumbents, leaving the establishment upbeat about midterm elections and the insurgent movement beaten but unbowed.

Tennessee Sen. Lamar Alexander's narrow win Thursday night and Kansas Sen. Pat Roberts' triumph on Tuesday dashed the tea party's last hopes of knocking out a sitting senator. Earlier this year, incumbents prevailed in Texas, Kentucky, South Carolina and Mississippi for a party intent on nominating viable candidates and winning Senate control in November's contests.

Republicans need to net six seats for the majority. Democrats currently hold a 55-45 advantage.

"The last two cycles we nominated some people who were not the best candidates for the general election," Senate Minority Leader Mitch McConnell, R-Ky., told reporters during a campaign stop in Hindman, Kentucky. "In 2014, I'm hard-pressed to think of a single state where we don't have the best nominee possible in order to do what this is all about, which is to actually get elected and make policy.

"We had a good cycle so far, it doesn't guarantee the outcome," he said.

Republicans blame tea partyers and flawed candidates for squandering the party's shot at Senate control in 2010 and 2012, especially in Delaware, Nevada, Colorado, Missouri and Indiana. Months ago, McConnell vowed to "crush" tea party candidates, and the National Republican Senatorial Committee invested money, staff and time, including more than 40,000 phone calls in Kansas in the final three weeks of the campaign.

Tea partyers and other outside groups acknowledged the beat down.

"If you kind of look at this like a baseball game, you guys totally struck out, done, you're gone," said Daniel Horowitz, a strategist who formerly worked with the Madison Project, one of several conservative groups that have spent money against GOP incumbents.

By comparison, tea partyers and outside groups upended Sen. Richard Lugar of Indiana in 2012. The 2010 midterms claimed Sen. Bob Bennett of Utah, who lost at a party convention, and Alaska Sen. Lisa Murkowski, who later won re-election as a write-in candidate.

But Horowitz and others insist that the numbers fail to account for the movement's success in forcing incumbents to move right on issues such as immigration, federal spending and reauthorization of the Export-Import Bank, the government agency that provides loans, loan guarantees and credit insurance to help foreign buyers purchase American-made products.

Business groups are pushing hard for the bank's renewal, but conservative groups are opposed, saying it amounts to corporate welfare.

Tea partyers say they have co-opted the Republican Party, especially the rank and file in the House who last week forced the leadership to allow a vote on legislation rolling back a program for young immigrants leaving here illegally that the GOP establishment has embraced. The House passed the measure.

"If we're just a bunch of crazies who can't gain any traction, they wouldn't worry about us," Horowitz said of the Republican establishment. Instead, he said, the movement has "converted people without firing a shot."

Republicans have nominated tea party and establishment-backed candidates in open seat races — Ben Sasse in Nebraska, Joni Ernst in Iowa and Steve Daines in Montana.

Tea partyers and other groups said some of their little-known candidates faced a daunting task, running against entrenched, well-funded incumbents who had far better name recognition. Despite those odds, Kansas' Milton Wolf held Roberts below 50 percent. In fact, Wolf's percentage combined with two other primary candidates totaled more than what Roberts registered.

Alexander also was held below 50 percent in his primary.

"People get caught in a system become risk-averse and change-averse," said Sal Russo of the Tea Party Express.

Particularly galling for the GOP establishment was the millions of dollars spent by outside groups against GOP incumbents in past election cycles and this year — money that could have been used to target Democrats. On Friday, Republicans made clear that any victory lap would wait until November, but the animosity toward the outside groups had not diminished.

Brad Dayspring, a spokesman for the National Republican Senatorial Committee, said the frustration is with "DC-based for-profit cannibal conservative groups that spent over $20 million against Republican candidates and have not a single thing to show for it. These groups, like Senate Conservatives Fund, actually say that winning doesn't matter, which in some weird way might explain their eagerness to back fringe, irrevocably flawed candidates who have now proven incapable of winning general elections and primaries as well."

The groups aren't backing down.

"Our enthusiasm is not going to be diminished because we came up short in some races," said Kevin Broughton, spokesman for the Tea Party Patriots, who said the group would redouble its efforts.